In 1972, a belt driven tape cartridge design (U.S. Pat. No. 3,692,255, issued to Robert A. Von Behren) was introduced for use in the computer industry for digital tape recording. Cartridges commonly in use in 1972 were approximately 100 mm by 150 mm and the magnetic tape was 6.35 mm (0.250 inches) wide. Cartridges of that size and corresponding drive mechanisms are still commercially available. In 1976, smaller data cartridges were developed, as described by Alan J. Richards, Mini Data Cartridge: A Convincing Alternative for Low-Cost, Removeable Storage, Hewlett-Packard Journal, May, 1976. The mini-cartridge size is 63.5 mm by 82.5 mm. Versions of the mini-cartridge are commercially available from a variety of vendors with tape widths varying from 3.81 mm (0.150 inches) to 6.35 mm (0.250 inches). New versions of mini-cartridges have been proposed having a tape width of 8.00 mm (0.315 inches). The external dimensions of the proposed cartridges are identical to existing mini-cartridges but there are numerous internal changes to accomodate wider tape.
Drive mechanisms for the the various belt-driven cartridge designs discussed above have a magnetic head that contacts magnetic tape within the cartridge through one opening in the front of the cartridge. In general, regardless of head position, the full width of the tape is supported by the magnetic head. However, if a cartridge containing 8.00 mm tape should be placed in a drive designed for 6.35 mm tape or narrower, the width of the head may not always support the full width of the wider tape. In particular, when the read/write gap of the head is at a track adjacent to one edge of the 8.00 mm tape, the head may not be wide enough to support the entire tape. If the tape overlaps a sharp edge on the head, the tape may be damaged. Therefore, there is a need to ensure that cartridges containing wide tape cannot be inserted into drives designed solely for narrower tape. There is a need to ensure that new drives can accept both narrow and wide tape cartridges. In addition, there is need to minimize changes to existing cartridge and chassis molds.
Each of the cartridges described above has a metal baseplate and a plastic cover. The cover has a top surface (the largest surface), a front surface having openings for accepting a magnetic head and drive roller in the drive mechanism, and two side surfaces. Each side surface has an elongated channel parallel to the metal baseplate with one side of the channel formed by an exposed portion of the metal baseplate. For alignment of the cartridge to the drive in a direction parallel to the metal baseplate of the cartridge, the drive chassis has an elongated guide corresponding to each of the channels in the cartridge sides. Vertical (perpendicular to the metal baseplate) alignment of the cartridge to the drive is accomplished by forcing the exposed portions of the metal baseplate against the lower surfaces of the chassis guides.
A pivoting door covers one opening in the front of the cartridge, with the pivot point in one corner next to one of the channels, and part of the door extends beyond the pivot point into the adjacent channel area. When the cartridge is inserted into a drive, the drive guide corresponding to the door pivot point engages the extension of the door so that the door is pivoted open as the cartridge is inserted.